1. Field of the Invention
This invention relates to an improved water guard for use in oil film bearings of the type employed in rolling mills.
2. Description of the Prior Art
As shown for example in U.S. Pat. No. 4,071,255, water guards have conventionally comprised circular elastomeric elements applied externally to the outer seal rings of oil film bearings. One such arrangement is illustrated in FIG. 1 where the roll 10 has an end face 12 joined by an intermediate tapered section 14 to a reduced diameter section 16 surrounded by a sleeve 18. The sleeve is keyed or otherwise secured to the roll neck, and is journalled in a bushing 20 fixed within a chock 22. Oil is supplied continuously between the sleeve and bushing, and a seal assembly generally indicated at 24 surrounds the intermediate tapered section 14 to prevent oil from escaping from the bearing and also to prevent externally applied cooling water and entrained contaminants such as dirt, mill scale, etc. from penetrating into the bearing.
The seal assembly 24 includes a flexible flanged neck seal 26 and an inner sealing ring 28, both of which are carried on the roll for rotation therewith, and a seal end plate 30, outer seal ring 32 and water guard 34 all of which are fixed in relation to the chock 22. This sealing arrangement is well known to those skilled in the art, and thus little if any further explanation is required, except perhaps with regard to the water guard 34 and the outer seal ring 32.
The primary role of the water guard is to provide the first line of defense against the unwanted and potentially damaging ingress of cooling water and entrained contaminants into the bearing. The role of the outer seal ring 32 is a bit more diverse. This component cooperates with the inner seal ring 28 to establish a sealing labyrinth leading to a drain opening 32a. The outer seal ring also serves as the support for the externally applied water guard 34. Additionally, however, when the bearing is being removed from the roll neck, the outer seal ring 32 contacts the inner seal ring 28 and exerts through it a force sufficient to pull both the inner seal ring and the neck seal 26 off of the roll neck. Also, it will be understood that during rolling, the roll neck on the non-thrust side of the roll will have a tendency to shift or "float" axially with regard to the chock 22 due to thermal expansion, mechanical tolerances, etc. If kept within acceptable limits, this axial floating does not damage the bearing. The importance of the outer seal ring 32 in this regard is that it serves as a stop against which the roll end face 12 can abut to limit axial floating and thereby safeguard internal bearing components from damage that might otherwise occur.
In order for the water guard 34 to provide an effective seal, its resilient lip 34a must be in continuous sealing contact with the roll end face 12. This, however, limits the extent to which the rolls can be reground to compensate for normal wear. For example, in the arrangement shown in FIG. 1, it is impossible to reduce the roll diameter to less than D.sub.1 without destroying the sealing relationship between the water guard lip 34a and the roll end face 12. Were it not for this limitation, the roll could undergo further reductions in diameter to about D.sub.2, thus considerably extending useful roll life.
In order to increase useful roll life, bearing designers have proposed an alternate water guard design of the type shown in FIG. 2. Essentially, this design eliminates the outer seal ring (32 in FIG. 1) in favor of a modified water guard generally indicated at 36 and consisting of an elastomeric member 38 bonded to and reinforced by a circular metal stamping 40. While this design does permit a beneficial further reduction of roll diameters to D.sub.2, it suffers from other serious deficiencies. Of particular concern is the relative fragility of the circular metal stamping 40 as compared to the outer seal ring 32 of the FIG. 1 arrangement. Although the metal stamping 40 can exert the force required to pull the inner seal ring 28 and neck seal 26 off of the neck when the bearing is being removed, it is not sufficiently sturdy to act as a float limiting stop. Thus, when the roll has a tendency to float excessively, causing the roll end face to come up against the water guard 36, the metal stamping 40 undergoes deformation, and because the stamping is essentially non-resiliant, this deformation is permanent. This not only results in the water guard being irreparably damaged, but it also raises the possibility that other internal bearing components may become damaged as the roll floats beyond safe limits.
To avoid these problems, bearing designers have proposed a still further modification as shown in FIG. 3. Here, the water guard 42 again consists of an elastomeric member 44 bonded to and reinforced by a metal stamping 46. The stamping is mounted in a recess 48 in the seal end plate, and a protruding shoulder 50 on the seal end plate serves as a float limiting stop. The stamping 46 again has sufficient rigidity to exert the required pulling force on the inner seal ring and neck seal.
Although this third modification is an improvement over those shown in FIGS. 1 and 2, it too suffers from serious drawbacks. For example, the metal stamping 46 remains non-resilient, relatively fragile, and thus susceptible to permanent damage during mounting of the bearing on the roll neck. For example, if there should be a misalignment of the bearing and the roll neck during mounting, the roll end may come into contact with the water guard 42, causing the reinforcing metal stamping 46 to become permanently deformed. Should this occur, the effectiveness of the water guard will be adversely affected, necessitating its immediate replacement. An additional drawback with this design, as well as with the design shown in FIG. 2, is that it is extremely difficult to achieve a reliable bond between the elastomeric portion of the water guard and the metal reinforcing portion. Experience has demonstrated that coolant attack, coupled with the high torsional forces to which the water guard is subjected, often destroys this bond, causing the elastomeric portion to be stripped away from the metal stamping. When this occurs, the effectiveness of the water guard is destroyed and immediate replacement is required.